This invention generally relates to marine recreational watercraft propulsion, and more particularly, to a power transmission device that transfers power from a single inboard engine, to multiple spaced apart impellers.
It is well known throughout the boating industry that the propelling of a watercraft with at least two spaced apart impellers offers significant advantages over the propelling of a craft with only one impeller. The use of multiple spaced apart impellers, with independent forward and reverse thrust control, can vastly improve low speed docking maneuverability. The use of multiple impellers can improve speeds and the handling of watercraft as well. There are many more advantages of using multiple spaced apart impellers. More will become evident throughout this disclosure.
The long time, and still current practice within the boating industry, is to align and couple a singular inboard engine to a singular impeller drive. Therefore to achieve the benefits of multiple impellers, one must also install multiple engines. This unfortunately is not practical, or even possible in smaller and less expensive watercraft.
To try and remedy this situation, several devices were invented. These inventions provide means for the connection of a single inboard engine to two or more independent impeller drives. This concept potentially provides for the advantages of larger multi-engine crafts within the smaller single engine crafts. Despite many attempts however, none have ever been deployed in common use throughout the recreational boating industry. This includes inventions by Wosenitz (U.S. Pat. No. 2,371,013) filed in March of 1943, to the more recent invention by Caricof, et al. (U.S. Pat. No. 5,649,8440) issued on Jul. 22, 1997. The prior arts have all failed in this regard due to some known design shortcomings, which the present invention overcomes.
In the field of this invention, as best as currently known, the only power transmission device that provides a stand-alone modular type of arrangement is the invention by Caricof et al. For the purpose of this disclosure, a stand-alone type of arrangement is one where the components of the power transfer system are basically assembled into a modular form, or device. The stand-alone arrangement is needed to allow universal application in various manufacturers"" watercrafts, with various types of engines and impeller drives. To be successful however, this arrangement must also be designed to allow use of the most current installation practices. Inventions such as the one by Wosenitz, and one by Sable, (U.S. Pat. No. 3,289,628) do not use a stand-alone arrangement, which prevents widespread acceptance of these inventions for use throughout the industry, especially within the recreational boating industry.
The invention by Caricof, et al., entitled DUAL DRIVE FOR POWER BOATS comes closest to providing an acceptable device, but falls short due to a few, but critical design shortcomings. The invention comprises a housing, supporting three main shafts, which are one input shaft and two output shafts. The shafts are connected for rotation by chains. Engine power enters through the input shaft, then exits out the two output shafts, for driving of two impellers. The shortcomings are explained below.
The first shortcoming of this prior art is the use of chains and sprockets. Chains by definition are a series of metal links connected to one another, used for transmission of mechanical power. The use of chains, for the purpose of powering a marine watercraft, requires continuous lubrication. This in turn requires the use of an oil filled and tightly sealed enclosure, or housing, as the inventors illustrate. This presents issues and concerns to the industry, which include concerns of leaks, ingress of moisture, corrosion, and oil contamination, which all lead to reliability problems. Furthermore, it provides difficulties in servicing and maintaining the device, especially within the very limited confines of a marine engine compartment.
A second shortcoming is the use of three shafts. With chains, this requires use of two separate chains with two sets of sprockets, adding additional and unwanted, weight, size, and cost to the device. This is unacceptable when considering use in small, and low cost watercrafts.
Thirdly, the inventors also teach to mount the two output shafts utilizing non-concentric adjustable bearing housings, allowing for varying of the axes of rotation. Adjustment is required with the use of chains, for the periodic take-up of chain slack. Removal of slack is accomplished through the varying and increasing of the spacing, or center distance, between the shafts. The adjustable bearing housings are the inventors"" means to remove slack after assembly, then to periodically adjust for the wear and stretch of the chains throughout the life of the device. In a device such as this, wear and stretch are accelerated by the high centrifugal forces, caused when moving heavy chains through the speeds observed within this type of transmission device. Periodic adjustments must therefore be made to minimize backlash, and to prevent disengagement of the chains from their sprockets. The need for this adjustment is one of the greatest shortcomings of this particular prior art. This is also true for any other prior art utilizing chains, or using this type of adjustment. The reasons are explained below.
Adjusting of shaft center distance within a marine engine compartment would be very difficult, but even more important is that the adjustment eliminates the ability to employ this device in practice with today""s direct plug-in type of impeller drives. These drives, which are also referred to as plug-in sterndrives, are the ones most demanded by the industry for use within inboard powered recreational watercraft. This type of drive however, requires for precise, and permanent location of the transmission output shafts. This is necessary to maintain concentric alignments between the transmission and the impeller drives which are mounted to the hull of the craft, specifically between the transmission output shafts, and the impeller input shafts, which insert directly into couplings mounted on those output shafts. This plug-in arrangement is demanded because it is the most compact and most cost efficient means of connection to a sterndrive today. This method will be illustrated and discussed in more detail later.
Furthermore, one cannot employ this device with any impeller drive in the smaller recreational watercrafts. This is due to the additional room required for significant lengths of universal drive shafts, needed to transfer power from the device to the impeller drives. Caricof et al. in their FIG. 1, as parts 17 and 19, illustrate these lengthy drive shafts. These long shafts must be used to compensate for misalignments caused by the adjustments in shaft center distance.
Accordingly, when considering use of this prior art, especially within the smaller and less expensive recreational watercrafts, the shortcomings are:
a) the excessive weight, size, and cost associated with the use of multiple sets of heavy steel chains and sprockets;
b) the additional complexity and cost of using a second output shaft, with all its associated parts;
c) the need and concerns of continuous lubrication;
d) the requirement for a tightly sealed and oil filled enclosure;
e) the need for periodic and difficult maintenance;
f) and, this unacceptable adjustment in shaft center distance.
Improvements and Advantages of the Present Invention
A collection of several features was assembled to overcome the shortcomings of the above prior art, as well as other prior arts. In addition, further improvements have been developed to help promote the use of the present invention throughout the boating industry. These will be discussed below and throughout the remaining sections.
The first feature for improvement is a synchronous belt. In contrast to a series of metal links, a belt by definition is a continuous band of tough flexible material. This allows assembly of a corrosion free, oil free, and maintenance free belt drive system. Use of any belt to transfer power instead of chains or gears, eliminates the need for continuous lubrication, seals, gaskets, and a leak proof enclosure. Through use of a synchronous type bed it further eliminates concern for slip, wear, backlash, and any need for future adjustments. Discussion of a third improvement below will explain how a synchronous belt can be utilized successfully in a high power transmission device such as this. But, before that discussion, additional reasons, and advantages encouraging use of this belt are as follows.
The synchronous belt, with its gear shaped teeth for positive engagement into matching type pulleys, was selected over all other type of belts. These included v-belts, multi-ribbed belts, flat belts, and the others. The synchronous belt was selected because it can eliminate all concern for slip. Slip reduces driveline efficiency and induces heat build-up. That leads to reliability and fire safety concerns, not acceptable for consideration in any watercraft. Gears could have been selected to prevent the slip, but a belt must be used to allow the flexibility needed to space the impeller drives at various distances, without concern for gear size, weight, changes in ratio, and again, a need for continuous lubrication.
The synchronous belt is also preferred because it operates at higher efficiencies than gears, or chains, or the other belts. It also operates at a lower noise level. This is a benefit to the industry to help maximize fuel efficiency, and in meeting the tighter noise limit regulations.
The light weight characteristic of the synchronous belt allows for reductions in the physical size, strength, and cost of components compared to using chains and gears. An example would be the preferred use of aluminum pulleys verses the heavy steel sprockets of the prior art. The lighter weight belt also reduces the centrifugal forces generated from the motion of itself, allowing use of long belts and higher rotational speeds than heavy chains allow. This allows the possible use of the present invention with some of today""s highest performing engines.
By allowing use of long belts, it also provides for an all-new capability and product line opportunity within the recreational boating industry. The lightweight synchronous belt allows use of the present invention in multi-hulled tunnel crafts known as catamarans. Catamarans utilize two spaced apart sections of hulls. They are typically manufactured with an engine and impeller drive mounted at each hull. This then provides for an unobstructed tunnel area between the hulls. In high performance catamarans, the tunnel is used to produce aerodynamic lift, lifting the craft partially out of the water. This effect significantly reduces the wetted surface area, and in turn the frictional drag on the hulls. That in turn, allows for greater speeds than can ever be achieved by conventional hulled watercrafts. Because of this superior performance benefit, consumers have demanded that the industry build a lower priced, single engine catamaran. However, to meet the overall performance requirements, they have had to add a third and centrally located section of hull, called a center pod, located down the bottom center of the boat. This third hull is used to support the conventional single engine, single impeller drive arrangement, in a low mounted position that provides for best overall performance. The two major shortcomings of this type of design are that the center pod reduces the available unobstructed tunnel area for providing aerodynamic lift, plus, because it also rides in the water, adds additional drag and power loss to the craft. This has been the accepted norm, even with a significant compromise in performance, until now.
Through use of a synchronous belt to transfer power over greater distances, two impeller drives can now be installed on the spaced apart hulls. At the same time, the economical single engine package can be installed to power the two impellers. The present invention can now provide for the manufacturing of a true, single engine catamaran type of watercraft. This watercraft can now have the same superior performance benefit, the unobstructed tunnel, that the higher priced multi-engine catamarans have had a monopoly on for years. In addition, the spaced apart impeller arrangement improves high-speed stability, low speed handling and performance, and docking maneuverability.
A second feature for improvement is a new multi-purpose shaft. This is referred to as a throughput shaft. The throughput shaft is used in place of a dedicated single purpose input shaft as in the prior art. This new shaft may be used in a multitude of ways. The throughput shaft is designed in such a way as to first deliver power into the present invention. The throughput shaft may then be used to either transmit a proportional amount of power directly through itself, to power an impeller drive, or to operate or power an auxiliary device or other piece of equipment, or it may even be used to do no secondary function at all. This option can provide an advantage in a twin-engine watercraft where two engines and a total of two impeller drives are still preferred. The advantage in this case could be to offset each of the impeller drives closer to each other, in a closeness never before achievable without staggering of the engines. This allows for performance improvements never before realized, which will be discussed later in this disclosure. If however the throughput shaft is used to power a second impeller drive, it can eliminate the necessity for a second separate output shaft as in the prior art. This avoids the increased complexity, manufacturing cost, and increased weight of providing a third shaft. Additionally, by elimination of that extra shaft, pulleys, bearings, etc., it allows for a more compact space requirement for application of the present invention in smaller, and lower priced, watercrafts.
A third and key improvement is the permanent fixing of shaft centerline locations. All the power delivery shafts of the present invention can be assembled and permanently located in a final position, for use in those positions throughout the life of the device. No adjustments in center distances will ever be required. This fixing of shaft locations is made possible in part through the use of a synchronous belt, however, to allow successful application of a synchronous belt, especially in a high power transmission such as this, the belt must be employed in combination with a means which applies a predetermined and critical amount of tension preload into that belt. This is key, because it will allow use of those demanded plug-in type of impeller drives. Below is an explanation of why, and how a synchronous belt can successfully be employed.
It is commonly assumed, and in most cases correctly assumed, that a synchronous belt can be used to control position of equipment, maintain synchronous timing of components, or to drive certain power devices while never needing any maintenance or adjustment, and most likely, never needing replacement. In comparison, chains must routinely be maintained, adjusted, and eventually replaced. This is required to rid a system of excess slack and prevent possible disengagement of the chain during its operation. This slack is caused by the wear within the metal links that make up the chain. A belt on the other hand has no metal links. It will not wear in a manner to cause this excess slack. This is made possible by the elastic properties of the materials that make up a belt. These properties also allow a belt to accept a significant amount of tension, without the fear of inducing failure as it does in chains. This leads to one of the most important discussions in this disclosure.
During the propelling of a watercraft, where submerged sections of hull are subjected to continuous drag, the power source and all the power transmission devices connected to that source are subjected to a continuous load condition. This load also increases exponentially with respect to increases in watercraft speed. This type of severe duty is what has made the successful employment of a belt drive transmission system within a marine watercraft so difficult to achieve, which brings up a very important point.
If a synchronous belt can be installed in a device, with a predetermined amount of tension preload placed into that belt, of sufficient magnitude to at least equal the tension that would be generated in that belt during maximum power transfer, plus, an amount equal to the additional tension that would be generated by the centrifugal force of moving that belt about the transmission at maximum operating speed, then that preloaded tension would prevent any further elongation of that belt, throughout the entire operating range of the device.
Prevention of further elongation within a belt will eliminate two effects that can cause failure in a belt drive system of this type. The first effect that can cause failure is cyclic elongation, or the stretching and relaxing of a belt each time it completes its path within the transmission. If not prevented, a failure mode called cyclic fatigue can occur, which is the progressive fatigue failure of the individual reinforcing fibers within the belt. This is similar to the breaking of a paper clip when flexed back and forth repeatedly. The second effect that will cause failure, is belt elongation or stretching on the tight side of the belt drive system whenever the belt is being pulled hard under load, causing the slack side of the belt drive system to go relaxed, as if an apparent excess length of belt was delivered to the slack side. This effect causes looseness of the belt around the drive pulley. This can then lead to the slipping and jumping of the belt teeth over the drive pulley, leading to tearing and wearing of the teeth, leading to eventual failure of the teeth. That is why chains and gears, with their relatively inelastic properties, have typically been the choice for high power, severe duty marine transmission devices. However, through continuous development of new belt materials and reinforcement fibers, higher magnitudes of tension preload are now being able to be applied, and can be taken advantage of by using the method explained below.
By comparison of a belt manufacturers"" data, in conjunction with standard centrifugal force and horsepower conversion equations, one can calculate for any given power application, and for any particular synchronous belt, the tension preload that will prevent further elongation of that belt. If the belt manufacturer will state that the belt can be operated continuously at the corresponding levels of stress, then the above described modes of failure can be completely avoided. This can finally allow use of a belt drive power transmission system in a watercraft, to allow the fixing of the shaft centerlines. This in turn allows use of the present invention with those direct plug-in types of impeller drives. The features of the present invention to provide for this tension preload will be discussed in more detail later within this disclosure.
It should also be pointed out that through application of the throughput shaft as described in this invention, to transfer a proportional amount of power directly through itself, say to drive another impeller, the remaining portion of the power is all that must be transferred by a belt. This allows for greater overall power transfer through the present invention than one might initially think based on the limits of a belt.
It must further be noted that the present invention can also be employed with any of the other types of propulsion drives, such as jet drives, surface drives, and others, beyond the plug-in type sterndrives discussed and illustrated in this discosure for the purpose of describing the present invention.
Objects of the Present Invention
Accordingly, to overcome the shortcomings of the prior art, the objects of the present invention are:
a) to reduce the weight, size, and cost of a transmission through use of a synchronous belt, a multi-purpose throughput shaft, and lighter components;
b) to provide a simplified and lower cost transmission by eliminating the need for a second output shaft and all its associated parts;
c) to provide a corrosion free and oil free transmission;
d) to provide a transmission free of gaskets, seals, and the need for a tightly sealed enclosure;
e) to provide for maintenance free operation;
f) to provide fixed placement of transmission shafts, allowing use with direct plug-in sterndrives, plus use in smaller, less expensive, watercrafts.
Additional objects of the present invention are:
g) to provide a transmission which is backlash free;
h) to provide improved operating efficiency and lower noise levels;
i) to provide a bet driven power transfer device, usable in this severe duty marine application;
j) to create entirely new product line opportunities within the boating industry.
Further features and advantages of the present invention will become better understood when considered with the subsequent descriptions and illustrations.
The present invention is a stand-alone power transmission device, comprising a housing, a throughput shaft, plus at least one output shaft spaced apart from said throughput shaft, a pulley system including at least one synchronous belt rotatively connecting said throughput shaft to said output shaft, means to allow for the transfer of power into or out of each said shaft, and means to preload a predetermined amount of tension into said synchronous belt, whereby said transmission may now allow fixed placement of the transmission shafts, in turn allowing use with plug-in type impeller drives, and in a compact manner sufficient to allow use in smaller recreational watercraft.